Engineering, School ofhttps://hdl.handle.net/1842/96
Fri, 05 Jun 2020 22:44:52 GMT2020-06-05T22:44:52ZHybrid rotational femtosecond/picosecond coherent anti-Stokes Raman spectroscopy of nitrogen at high pressures and temperatureshttps://hdl.handle.net/1842/37092
Hybrid rotational femtosecond/picosecond coherent anti-Stokes Raman spectroscopy of nitrogen at high pressures and temperatures
Mecker, Nils Torge
In this thesis, the use of two-beam hybrid rotational femtosecond/picosecond coherent anti-Stokes Raman spectroscopy (HR-CARS) for temperature measurements in nitrogen gas at high pressures (1-70 atm) and temperatures (300-1000 K) is demonstrated.
An experimental setup for 1 kHz measurements of well-resolved frequency-domain HR-CARS spectra across all investigated pressures and temperatures was built. To achieve the required spectral pump/Stokes excitation bandwidth, a pulse shaper was used to create an almost transform limited 42 fs pump/Stokes pulse at the interaction volume, after having passed through a 28 mm fused silica window of a high pressure cell. To obtain nonresonant background free spectra at the required spectral resolution, a narrow-bandwidth, frequency-upconverted 5.5 ps probe pulse was created in a beta barium borate (BBO) crystal (Type 1) via sum frequency generation (SFG) using second harmonic bandwidth compression (SHBC).
A computational code has been developed to model S-branch HR-CARS spectra and fit to experimental results to obtain best-fit temperatures. The model spectra are based on transition frequencies calculated from a non-rigid rotor approximation, taking rotational-vibrational interaction into account. Linewidths are taken from published measurements and interpolated to the required temperature. The model assumes impulsive pump/Stokes excitation and the probe pulse is modelled with chirp, as this was observed experimentally. The fitting is done through a nonlinear least-squares algorithm.
Good qualitative fits, including good accuracy and precision between thermocouple measured and best-fit temperatures over all the explored pressure and temperature regimes are shown. Across all experimental spectra, the average percentage temperature difference between best-fit and thermocouple measured temperatures (as a percentage of the thermocouple measurement), is -0.3% with a standard deviation of 7.1%.
Overall, accurate nitrogen thermometry is demonstrated, showing the suitability of HR-CARS for characterising high pressure and temperature environments.
Fri, 03 Jul 2020 00:00:00 GMThttps://hdl.handle.net/1842/370922020-07-03T00:00:00ZKinetic model of a CO2 recycling rotary adsorption wheel for gas turbine power plants with carbon capturehttps://hdl.handle.net/1842/37091
Kinetic model of a CO2 recycling rotary adsorption wheel for gas turbine power plants with carbon capture
Palfi, Erika Alexandra
The selective recycling of carbon dioxide (CO2) upstream of post-combustion capture
processes can greatly reduce both the size of equipment and capital costs by process
intensification. For combined cycle gas turbine (CCGT) power plants, flue gas flow rates can
be lowered by two thirds and CO2 concentration greatly increased from 4% to 14% v/v.
Selective recycling of carbon dioxide (CO2) can be achieved in CCGT plants with a low pressure
drop, regenerative rotary CO2 transfer device using physical adsorption. A newly developed
kinetic model of this CO2 transfer device shows that, for an activated carbon material with
suitable equilibrium properties, a mass requirement of circa 600 tonnes is necessary for a
new build CCGT plant of 800 MW with 90% capture. This is 3.7 times higher than the mass
previously reported, by means of an equilibrium model, for the best performing
commercially available activated carbon material.
A rigorous design shows that the mass of 600 tonnes of activated carbon can be distributed
on a honeycomb structure on two CO2 transfer wheels of 30m diameter and 2.2m height,
rotating at 1rpm, with a preferential direction of leakages towards the flue gas side. The
design then provides the basis for an optimisation study of CO2 recovery rate and adsorbent
mass by examining first kinetic properties of the CO2 adsorbent to inform material
development and research; second, rotational speed; and, last, the partitioning of the wheel.
Further, the selective recycling of CO2 is examined as a retrofit option for CCGTs with solvent
based post-combustion capture. The aim is to explore the possibility to increase overall
capture level beyond the initial design of 90% capture using an integrated model consisting
of a gas turbine combined cycle, a rotary CO2 transfer device and a post-combustion capture
unit and compression train. The operation of the absorber column at reduced gas velocity is,
however, shown to be detrimental to retrofitting selective CO2 recycling to existing CCGT
plants with solvent-based capture.
Finally, a comparison between a new build CCGT with PCC and fully integrated regenerative
selective CO2 transfer wheel to a new build CCGT with PCC without SEGR is performed. The
results show a possible reduction in absorber total packing volume of 42% and a marginal increase of net power output of 0.3% relative to a new build CCGT with PCC without SEGR.
Fri, 03 Jul 2020 00:00:00 GMThttps://hdl.handle.net/1842/370912020-07-03T00:00:00ZComplex dynamics of solid-fluid systemshttps://hdl.handle.net/1842/37085
Complex dynamics of solid-fluid systems
Essmann, Erich
The focus of this thesis was the investigation of the complex dynamics of solid-fluid systems. These systems are of great industrial importance, such as in methane clathrate formation in sub-sea pipelines. As well as being crucial to furthering our understanding of various natural phenomena, such as the rate of rain droplet formation in clouds.
We began by considering the problem of the orbits tracked by ellipsoids immersed in viscous and inviscid environments. This investigation was carried out by a combination of analytical and numerical techniques: direct numerical simulations of resolved full-coupled solid-fluid systems, analysis the Kirchhoff-Clebsch equations for the case of inviscid flows, and characterising dynamics through advanced techniques such as recurrence quantification analysis. We demonstrate that the ellipsoid tracks a chaotic orbit not only in an inviscid environment but also when submerged in a viscous fluid, under specific conditions. Under inviscid environments, an ellipsoid subject to arbitrary initial conditions of linear and angular momentum demonstrates chaotic orbits when all the three axes of the ellipsoid are unequal, in agreement with the Kozlov and Onishchenko’s theorem of non-integrability of Kirchhoff’s equations and also with Aref and Jones’s potential flow solution.
We then extended our methodology to understand the dynamics of a single ellipsoid tumbling in a viscous environment with the presence of both passive and viscosity coupled tracers in addition to the chaotic dynamics predicted by the Kirchhoff-Clebsch equations. Our results show that the bodies move along from viscosity gradients towards minima of the viscous stress. These bodies might become trapped in unstable minima. However, more work is needed to understand the long-term mixing of viscosity coupled tracers. Our direct numerical solver was also extended to include contact models for solid-solid interactions in the simulation domain. The validation of the contact models was presented.
Finally, we expand, the theoretical framework of the Kirchhoff-Clebsch equations to account for the presence of multiple bodies. This extension was done by using Hamiltonian mechanics to extend the derivation proposed by Lamb. We present our preliminary result of simulating two solids systems using the extended Kirchhoff-Clebsch equations. The rel- ative orientations of the two solids were found to regularly switch from being correlated to anti-correlated in an otherwise chaotic system. Further work is required to understand the mechanism behind this behaviour.
Fri, 03 Jul 2020 00:00:00 GMThttps://hdl.handle.net/1842/370852020-07-03T00:00:00ZQuantifying and reducing uncertainty in tidal energy yield assessmentshttps://hdl.handle.net/1842/37078
Quantifying and reducing uncertainty in tidal energy yield assessments
Clayton, Robert Vivian
Tidal stream energy has the potential to contribute to a diverse future energy mix. As the industry moves towards commercialisation and array scale deployment, there is an opportunity to better understand the uncertainties around energy yield assessments. Energy yield assessments are used widely in the wind industry to evaluate the potential energy production from a prospective project. One of the key challenges is to quantify and reduce uncertainty in energy yield assessment. This thesis investigates ways to achieve this through utilising lessons learnt from the established wind industry. An evaluation of both the wind and tidal energy yield assessment process is conducted, highlighting where synergies can be used to increase understanding of uncertainty for the nascent tidal industry.
The processes are comparable starting with a campaign to collect site data to characterise the resource at the measurement location. The next stage is to evaluate the long term variations, however this is where the two methods differ. Analysis of long term wind effects requires correlations to be made between short term site data and long term reference data from alternative sources. An assessment of tidal variations over longer periods utilises harmonic analysis, which is capable of deconstructing the individual astronomical variations of the tide and reconstructing them to predict future variations.
Despite harmonic analysis being able to determine the astronomical effects of the tide, there are uncertainties in the measurements of tidal flow which are associated with non-astronomical effects. Effects such as turbulence introduce uncertainty when evaluating measured tidal data. This is one area which is investigated further in the thesis. Methods to evaluate the turbulence intensity from real ADCP data are investigated.
The next stages require creating a numerical model of the site to extrapolate the data spatially to other areas of interest (such as a turbine location). Energy yield predictions for both wind and tidal are made by combining a power curve with the long term resource. The energy yield outputs are then adjusted to account for energy losses and uncertainties are applied to produce final energy yield values with the attributed probability values associated.
Statistical methods are applied to harmonic analysis to assess the level of uncertainty in long term predictions of tidal variations. A method using spectral analysis is applied to evaluate the residuals between measured and modelled data and proves to be accurate at determining missing tidal constituents from the analysis. A method for evaluating the turbulence intensity of the flow is shown, to better understand the stochastic nature of the tidal signal. An investigation is conducted to assess the propagation of bed friction uncertainty, in hydrodynamic modelling, and the resulting impact on the predicted power output from a theoretical fence of tidal turbines spanning a tidal channel. The methodology is based on first conducting sensitivity studies by varying a parameter in the model and calculating the power. Then using a mean and standard deviation for the input parameter, the impact of the uncertainty can be transferred to the estimate of power. The results show that a larger uncertainty associated with the bed roughness tends to over predict the estimation of power.
This work aims to inform the standardisation of practices and guidelines in tidal resource assessment and to support developers, consultants and financiers in future tidal energy yield assessments. The final chapter includes procedural recommendations for future tidal energy projects, summarising methods to calculate uncertainty and recommendations to reduce them.
Thu, 19 Mar 2020 00:00:00 GMThttps://hdl.handle.net/1842/370782020-03-19T00:00:00Z